Electroimpedance tomography (EIT) is increasingly used in medicine. Typical EIT devices use 8, 16 or 32 electrodes for data acquisition, current being fed through two electrodes and the resulting voltage being measured between the remaining electrodes. By combining different feeds and measurements, it is possible to generate a signal vector, from which the impedance distribution can be determined by means of a suitable algorithm or the relative change in the impedance distribution relative to a reference value can be determined in the electrode plane in functional EIT (fEIT). The latter method is used in status-dependent functional electroimpedance of the thorax, in which N electrodes are arranged around the thorax in a ring-shaped pattern in order to reconstruct a tomogram of the ventilation-related relative impedance change, which is an indicator of the regional distribution of the ventilation of the lungs, from the comparison of the signal vectors in different states of the lungs, e.g., end-inspiratory and end-expiratory states. Thoracic fEIT is well suited for the regionally resolved lung monitoring of ventilation, especially in intensive care units in hospitals.
A device for electroimpedance tomography is disclosed, for example, in U.S. Pat. No. 5,919,142 A.
The so-called adjacent data acquisition, in which current is fed through two adjacent electrodes and the voltages between the remaining electrodes are measured adjacent to each other, wherein current-carrying electrodes are left out because of the unknown voltage drop over the current-carrying electrodes, is a frequently used data acquisition strategy. Thus, thirteen voltage values are obtained for a current feed position. Thirteen voltages are again obtained for the current feed via a subsequent electrode pair, so that a total of 16*13=208 voltage measured values are present, from which the impedance distribution or relative change in impedance distribution can be determined with the use of 208 reference voltages with a reconstruction rule, which is applicable to this form of data acquisition.
Electrode belts, which consist of a support structure, to which the electrodes are attached and held in position, are usually used to attach the electrodes to the body of a test subject. Such an electrode belt is known from the document EP 1 649 805 B1, which forms this class. The electrodes are in flat contact with the body of the test subject and have a contact means, to which an electrode feed line each is connected as a lead of a multiwire feed cable. The effect of interferences is reduced by shielding each electrode feed line.
The electrode belt is divided into two groups of eight electrodes each, which are contacted each to a separate, multiwire feed cable. The multiwire feed cable has two strands, with which four electrodes are contacted.
Magnetic fields, which compromise the voltage measurements, may develop due to the current feed at adjacent electrodes. This magnetic cross-talk is slight as long as the electrode feed lines affected extend within a single multiwire feed cable. If a multiwire feed cable is located on the right-hand side and left-hand side of the electrode belt, the magnetic cross-talk is slight as long as the electrode feed lines for the current feed and the voltage measurement extend exclusively in the right-hand or left-hand feed cable. The maximum cross-talk occurs if the electrode feed lines for the electrode pairs for current feed and voltage measurement electrode pairs extend in different feed cables.